The high severity-fluid catalytic cracking (HS-FCC) process has shown the potential for converting refinery streams containing heavy oils into product streams containing light olefins. These light olefins are suitable for producing large amounts of propylene and high-octane gasoline. The HS-FCC process is capable of producing yields of propylene up to four times greater than the traditional FCC units with greater conversion levels for a range of petroleum steams. Achieving maximum propylene yield and effective conversion from various feedstock with a wide range of qualities presents considerable challenges to the catalyst design for the HS-FCC. The conventional feedstocks for the FCC range from hydrocracked bottoms to heavy feed fractions such as vacuum gas oil and atmospheric residue. However, these feedstocks are limited and obtained through costly and energy intensive refining steps, and thus, not expected to fulfill the growing market demands.
A typical FCC catalyst consists of zeolite, active matrix (additive), inactive matrix (filler), and the binder. The first two components are the main drivers for cracking the feed in the process. The filler and the binder contribute to the overall activity of the catalyst by providing proper particle strength and morphology. Presence of zeolites in a HS-FCC catalyst improves the yield of light olefins due to its shape selectivity, special pore structure, and greater specific surface area. However, when the crystal size of the zeolites is close to the molecular diameter of light hydrocarbons, the diffusion of the reactant or product molecules within the micropores is usually the rate-limiting step of the reaction. Furthermore, coke formation on the crystal surface is favored under diffusion-controlled regime, which obstructs the accessibility of the pores, and thus deactivates the catalyst.